Parameters

host

Can be either a host name or an IP address. Passing the NULL value
or the string "localhost" to this parameter, the local host is
assumed. When possible, pipes will be used instead of the TCP/IP
protocol.

Prepending host by p: opens a persistent connection.
mysqli_change_user() is automatically called on
connections opened from the connection pool.

username

The MySQL user name.

passwd

If not provided or NULL, the MySQL server will attempt to authenticate
the user against those user records which have no password only. This
allows one username to be used with different permissions (depending
on if a password is provided or not).

dbname

If provided will specify the default database to be used when
performing queries.

port

Specifies the port number to attempt to connect to the MySQL server.

socket

Specifies the socket or named pipe that should be used.

Note:

Specifying the socket parameter will not
explicitly determine the type of connection to be used when
connecting to the MySQL server. How the connection is made to the
MySQL database is determined by the host
parameter.

OO syntax only: If a connection fails an object is still returned. To check
if the connection failed then use either the
mysqli_connect_error() function or the mysqli->connect_error property as in
the preceding examples.

Note:

If it is necessary to set options, such as the connection timeout,
mysqli_real_connect() must be used instead.

Note:

Calling the constructor with no parameters is the same as calling
mysqli_init().

Note:

Error "Can't create TCP/IP socket (10106)" usually means that the variables_order configure directive
doesn't contain character E. On Windows, if the
environment is not copied the SYSTEMROOT environment
variable won't be available and PHP will have problems loading Winsock.

User Contributed Notes 13 notes

Please do use set_charset("utf8") after establishing the connection if you want to avoid weird string issues. I do not know why the documentation does not warn you about this kind of stuff.

We had a hard time figuring out what was going on since we were using mb_detect_encoding and it said everything was UTF-8, but of course the display was wrong. If we used iconv from ISO-8859-1 to UTF-8 the strings looked fine, even though everything in the database had the right collation. So in the end, it was the connection that was the filter and although the notes for this function mention default charsets, it almost reads as a sidenote instead of a central issue when dealing with UTF and PHP/MySQL.

A friend of mine encountered a sudden bug with CMS Piwigo. I discovered that :- He had a hosting rule to use PHP 5.6.- The hoster uses 5.6.6, verified using phpinfo();.- The CMS declared a database name parameter as null.

That gallery CMS was unable to connect to MySQL and left only a warning message about it.

A far more secure and language independent way of connecting to mysql is to use the READ_DEFAULT_FILE options. This passes the workload over to the mysql library, which allows for the configuration file itself to be outside of the scope of the language.

The config file itself is something like this:[client]user=user_upassword=user_passwordhost=dbhostport=3306database=the_databasedefault-character-set=utf8

There's a separate port parameter, unlike mysql_connect. However, using host:port on the host parameter does actually work.

There is a caveat. If the host is 'localhost' then the port is ignored, whether you use a port parameter or the implicit syntax I mentioned above. This is because 'localhost' will make it use unix sockets rather than TCP/IP.

If you get an error like
Can't connect to MySQL server on 'localhost' (10061)
and you use named pipes/socket connections (or aren't sure how you installed the MySQL server) try the following connect command:

Just wanted to add a note for anyone looking to use the MySQLi persistent connections feature; it's important to note that PHP opens and retains one connection per database user per process.

What this means is that if you are hosting multiple applications, each with its own database user (as is good practice) then you will end up multiplying the number of connections that PHP may hold open.

For example, if you have PHP configured with a maximum of eight worker processes, and you regularly use four different database users, then your MySQL server will need to accept at LEAST a maximum of 32 connections, or else it will run out.

However, if you would like to minimise the number of connections, what you can do is instead is to open the connection using a "guest" user (with no privileges except logging in) and then use ->change_user() to switch to a more privileged user, before switching back to the guest when you're done. Since all of the connections would therefore belong to the guest user, PHP should only maintain one per worker process.

If you want to connect to local named pipe on windows and you get error "php_network_getaddresses: getaddrinfo failed: No such host is known. ", even if you using using "." as host, please check your if you are using mysqlnd driver: If this is true, then probably you need to update to version 5.4 of php:

So, life is good — you're connected to the database and executing mysqli methods. Except, life isn't good, because you aren't actually using database_b because myuser doesn't have any privileges on it. You won't catch this until you try to perform a later operation, when you'll get an error, "MYSQL Error: No database selected", and find yourself scratching your head and thinking "what do you mean, of course I have a database selected; I selected one when I called the constructor".

As a result, you may want to perform an additional check after connecting to mysql, to confirm that you're actually connected not just to the mysql server, but to the actual database: